The present invention relates to a cross polarized wave interference eliminating system and method and, more particularly, to a cross polarized wave interference eliminating system and method which eliminate cross polarized wave interference caused on the receiving side in microwave communication.
When the microwave communication lines of two routes are formed by using a vertically polarized wave (V-polarized wave) and horizontally polarized wave (H-polarized wave), which are orthogonal to each other, between stations, cross polarized wave interference occurs on the receiving side due to the influences of fading and the like. In order to eliminate such cross polarized wave interference, the receiving side notifies the transmitting side of transmission power control information in accordance with the reception state, and the transmitting side controls the transmission power of V- and H-polarized waves on the basis of the transmission power control information.
FIGS. 7 and 8 show a conventional cross polarized wave interference eliminating system. FIG. 7 shows the transmitting side. FIG. 8 shows the receiving side.
In this cross polarized wave interference eliminating system, first of all, reception determination devices 81 and 82 respectively detect reductions in the reception power of V- and H-polarized waves. Assume that when the reception determination devices 81 and 82 exchange signals, it is found that the reception power of a V- or H-polarized wave has decreased. In this case, in order to simultaneously control the transmission power of both V- and H-polarized waves, transmission power control information is notified through one of (or both of) a route formed by a transmitter 65, transmission/reception duplexer 51, antenna 52, antenna 32, transmission/reception duplexer 31, and a receiver 15 and a route formed by a transmitter 75, the transmission/reception duplexer 51, the antenna 52, the antenna 32, the transmission/reception duplexer 31, and a receiver 25, thereby simultaneously controlling the power of V- and H-polarized waves by simultaneously controlling transmission power controllers 41 and 42.
In such a conventional cross polarized wave interference eliminating system, however, since the transmission power of V- and H-polarized waves is controlled at the same time, it is impossible to obtain interference compensation characteristics optimal for cross polarized wave interference. Assume that one of the levels of V- and H-polarized waves increases, because transmission power control information is not used for cross polarized wave interference elimination, and the cross polarized wave interference amount increases while the cross polarized wave identification degree of an antenna has decreased. In this case, the compensation amount of an interference compensator is saturated, and hence the system cannot sufficiently exhibit its performance. In addition, even if it is required to increase the transmission power of one of polarized waves, control must be performed to increase the transmission power of both polarized waves, resulting in an increase in the power consumption of the apparatus.
In contrast, the powers of V- and H-polarized waves may be independently controlled. If, however, power control is simply performed for each polarized wave, the apparatus may operate in a direction to increase its own cross polarized wave interference amount owing to the execution of transmission power control.